Metal halide discharge lamp containing beryllium

ABSTRACT

A high-pressure electric discharge lamp which emits a continuous spectrum and containing beryllium, halogen and mercury. The lamp is operated at temperatures in the range of 300* to 700* C. to obtain white light emission of good color-rendering properties and brightness.

United States Patent [72] Inventors Saburo Ito; Shingo Ezaki, both of Ohtsu, Japan 869,554

Appl. No. Filed 3,259,777 7/1966 Fridrich..

Primary Examiner-Roy Lake 1 [22] Oct. 27, 1969 145] Patented Oct. 19, I971 I73] Assignec New Nippon Electric Company Ltd.

' Assistant Examiner-Palmer C. Demeo Attorneys-Norman J. OMalley and Owen J. Meegan |54| METAL HALIDE DISCHARGE LAMP CONTAINING BERYLLIUM 4 Claims, 2 Drawing Figs.

[52] U.S. 3I3/l84, ABSTRACT: A high-pressure electric discharge lamp which emits a continuous spectrum and containing beryllium, halogen and mercury. The lamp is operated at temperatures in the range of 300" to 700 C. to obtain white light emission of good color-rendering properties and brightness.

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. SHEET 20F 2 WAVELENGTH IN NANOMETERS SHINGO EZAKI. SABURO ITO jNVENT BY ATTO NEY BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high or super high pressure vapor discharge lamps, and more particularly to metal halide discharge lamps which radiate a continuous spectrum throughout the visible region.

2. Description Of The Prior Art In the past, such discharge lamps included metals such as thallium (Tl), sodium (Na), indium (In), scandium (Sc), or thorium (th), and since the emission spectra in the region of the visible rays are line spectra, the color-rendering properties can be improved. For example, the General Color-Rendering Index Ra, is 60 to 65 for a discharge lamp including mercury (Hg) and halides of T1, Na and In, and 70 to 80 for a lamp including Hg and halides of Se and Th.

SUMMARY OF THE INVENTION The present invention eliminates these defects and provides a discharge lamp wherein its color-rendering property is improved effectively on the basis of an entirely novel luminescent principle.

The inventors manufactured for trial a discharge lamp added with beryllium (Be) and submitted it to a series of tests wherein the temperature of the coldest portion of the tube wall was varied within the range of 200 to 300 C. As a result, at about 200 to 270 C. in temperature, the line spectra of Be (234.9, 313.1, 322.1 nm.) and of Hg (365.0, 404.7, 435.8, 546.], 578.9 nm, and so on) distinctly appeared at the same time, and both the color-rendering property and the efficiency were insufficient. At about 300C. the absorption of line spectra of Be and Hg began and a continuous spectrum was observed throughout the region of the visible radiation. Above about 400 C. the excellent color-rendering properties were found.

The reason for this change from a line to continuous spectra seems to be because, in the latter case, the line spectra of Be and the ultraviolet rays of Hg were self-absorbed under the influence of the vapor of beryllium iodide (Bel The energy was reradiated throughout the region of the visible rays, that is, the region of 400 to 700 nm. Because of this, the luminescent principle appears to be entirely different from that of the atomic luminescence as hereinbefore known.

It has been found that, on the other hand, when the temperature of the wall of the arc tube is more than 700 C. an absorption occurs in the visible region and a re-emission band masks the infrared radiation. Therefore, the color-rendering properties and the efficiency of the lamp are reduced considerably.

BRIEF EXPLANATION OF THE DRAWING FIG. 2 of the attached drawing is a spectral energy distribution diagram of one embodiment of the present invention and FIG. 1 is a cross-sectional view of a lamp using the fill ingredients which are described.

DESCRIPTION OF THE PREFERRED EMBODIMENT about 0.2:! and 4.011 preferably about 2.0: l. The halogen can be included as either the halide of mercury or of beryllium or as the element.

When the amount of Be added is greater than the upper limit, it may be de sited on the inner wall of the tube and absorb the lrg t, ort e are may be unstable. When the quantity is less than the stated lower limit, the re-emission phenomenon may be so slight and the line spectra of mercury or Be may be so strong, that it is impossible to get an excellent white light. In addition, the amount of halogen should be less than that which would fonn stoichiometric beryllium iodide or bromide.

Referring to FIG. I of the drawing, a lamp was prepared according to the present invention. The are tube I was 10 mm. (inner diameter), 8 mm. (length) and 1.2 cc. (volume). The fill of the lamp is described in table I. It was tested for the characteristics described in table II and illustrated in FIG. 2. As indicated, the only difference was the wall temperature of the lamp.

The high-pressure electric discharge lamp includes an outer vitreous envelope 2 of generally tubular form having a central bulbous portion, with a quartz arc tube supported within and surrounded thereby. The base 3 is of the usual screw type. Sealed in the arc tube 1 at the opposite ends thereof are main discharge electrodes 4 and 5 which are connected to the start ingelectrodes 7 and 6 through respective resistors 8 and 9 for starting. Electric power source is supplied in a conventional manner from the base 3 for establishing arc discharge between the main electrodes 4 and 5.

Thus, the present invention is effective to produce a continuous spectrum based on a luminescent principle difi'erent from that of the atomic luminescence. Excellent color-rendering properties are obtained when using a filling of the halide of Be in the arc tube and maintaining the temperature of the tube wall (vapor pressure in the tube) at 300 to 700 C. during operation.

As our invention we claim:

1. A metal vapor discharge lamp characterized by an arc tube containing a fill of a quantity of halogen, mercury and beryllium together with inert gas, the interior wall of said are tube is maintained at a temperature in excess of 300 C. and no higher than 700 C. during operation.

2. The metal vapor discharge lamp according to claim I wherein said beryllium is present in quantities of 5.5Xl0'to 2.2XIO'gram atoms per cm. of arc tube volume.

3. The metal vapor discharge lamp according to claim 2 wherein the atomic ratio of said halogen and said beryllium is respectively between about 02:1 and 4.0: l.

4. The metal vapor discharge lamp according to claim I wherein halogen is iodine. 

2. The metal vapor discharge lamp according to claim 1 wherein said beryllium is present in quantities of 5.5 X 10 to 2.2 X 10 gram atoms per cm. of arc tube volume.
 3. The metal vapor discharge lamp according to claim 2 wherein the atomic ratio of said halogen and said beryllium is respectively between about 0.2:1 and 4.0:1.
 4. The metal vapor discharge lamp according to claim 1 wherein halogen is iodine. 